/*
author: Maksim1744
created: 26.04.2024 01:52:26
*/
#include "bits/stdc++.h"
using namespace std;
using ll = long long;
using ld = long double;
#define mp make_pair
#define pb push_back
#define eb emplace_back
#define sum(a) ( accumulate ((a).begin(), (a).end(), 0ll))
#define mine(a) (*min_element((a).begin(), (a).end()))
#define maxe(a) (*max_element((a).begin(), (a).end()))
#define mini(a) ( min_element((a).begin(), (a).end()) - (a).begin())
#define maxi(a) ( max_element((a).begin(), (a).end()) - (a).begin())
#define lowb(a, x) ( lower_bound((a).begin(), (a).end(), (x)) - (a).begin())
#define uppb(a, x) ( upper_bound((a).begin(), (a).end(), (x)) - (a).begin())
template<typename T> vector<T>& operator-- (vector<T> &v){for (auto& i : v) --i; return v;}
template<typename T> vector<T>& operator++ (vector<T> &v){for (auto& i : v) ++i; return v;}
template<typename T> istream& operator>>(istream& is, vector<T> &v){for (auto& i : v) is >> i; return is;}
template<typename T> ostream& operator<<(ostream& os, vector<T> v){for (auto& i : v) os << i << ' '; return os;}
template<typename T, typename U> pair<T,U>& operator-- (pair<T, U> &p){--p.first; --p.second; return p;}
template<typename T, typename U> pair<T,U>& operator++ (pair<T, U> &p){++p.first; ++p.second; return p;}
template<typename T, typename U> istream& operator>>(istream& is, pair<T, U> &p){is >> p.first >> p.second; return is;}
template<typename T, typename U> ostream& operator<<(ostream& os, pair<T, U> p){os << p.first << ' ' << p.second; return os;}
template<typename T, typename U> pair<T,U> operator-(pair<T,U> a, pair<T,U> b){return mp(a.first-b.first, a.second-b.second);}
template<typename T, typename U> pair<T,U> operator+(pair<T,U> a, pair<T,U> b){return mp(a.first+b.first, a.second+b.second);}
template<typename T, typename U> void umin(T& a, U b){if (a > b) a = b;}
template<typename T, typename U> void umax(T& a, U b){if (a < b) a = b;}
#ifdef HOME
#define SHOW_COLORS
#include "/mnt/c/Libs/tools/print.cpp"
#else
#define show(...) void(0)
#define debugf(fun) fun
#define debugv(var) var
#define mclock void(0)
#define shows void(0)
#define debug if (false)
#define OSTREAM(...) ;
#define OSTREAM0(...) ;
#endif
const ll inf = 1e18;
ll max_weights(int n, int m, std::vector<int> X, std::vector<int> Y, std::vector<int> W) {
int sz = maxe(Y) + 1;
vector<ll> dp1(sz + 1, -inf);
vector<ll> dp2(sz + 1, -inf);
vector<vector<pair<int, int>>> atx(n);
for (int i = 0; i < m; ++i) {
atx[X[i]].eb(Y[i], W[i]);
}
for (auto& v : atx)
sort(v.begin(), v.end());
dp1[0] = dp2[0] = 0;
for (int i = 0; i < n; ++i) {
vector<ll> next_dp1(sz + 1, 0);
vector<ll> next_dp2(sz + 1, 0);
int ind1 = 0;
ll cur1 = 0;
for (int h = 0; h <= sz; ++h) {
if (i) {
cur1 = max(cur1, dp1[h]);
next_dp2[h] = max(next_dp2[h], cur1);
next_dp1[h] = max(next_dp1[h], cur1);
if (ind1 < atx[i - 1].size() && atx[i - 1][ind1].first == h) {
cur1 += atx[i - 1][ind1].second;
++ind1;
}
}
}
int ind2 = (int)atx[i].size() - 1;
ll cur2 = -inf;
for (int h = sz; h >= 0; --h) {
if (ind2 >= 0 && atx[i][ind2].first == h) {
cur2 += atx[i][ind2].second;
--ind2;
}
cur2 = max(cur2, dp2[h]);
next_dp2[h] = max(next_dp2[h], cur2);
}
int ind3 = 0;
ll cur3 = 0;
for (int h = 0; h <= sz; ++h) {
next_dp1[h] = max(next_dp1[h], dp2[h] + cur3);
if (ind3 < atx[i].size() && atx[i][ind3].first == h) {
cur3 += atx[i][ind3].second;
++ind3;
}
}
swap(dp1, next_dp1);
swap(dp2, next_dp2);
}
return max(maxe(dp1), maxe(dp2));
}
#ifdef HOUSE
int main() {
ios_base::sync_with_stdio(false); cin.tie(NULL);
int n, m;
cin >> n >> m;
vector<int> x(m), y(m), w(m);
for (int i = 0; i < m; ++i) {
cin >> x[i] >> y[i] >> w[i];
}
cout << max_weights(n, m, x, y, w) << '\n';
return 0;
}
#endif
